very first episode finished, thank you! it was that period they switched to "real" plates in TV, ingo?

The plates seem indeed authentic, but the were no periods of fake and real plates - in German movies it was and still is common to use faked plates in movies and TV-series. In our plate-forum we even have pics of faked plates from pre-war productions (surely found here at IMCDb).

Der Nachtkurier meldet...: Season 1, Episode 4
Polizisten sind auch Menschen (12 Dec. 1964) Polizist/innen would be more correct today
and for the first time, i guess, we have a
***** giest in a **** rolle legendary Isar 12/vehicle_43054-BMW-501-1952.html
even same crew that retired from TV series Funkstreife Isar 12
german word for this kind of "recycling" is Anschlußverwendung